Continuously variable gear transmission

ABSTRACT

A continuously variable gear can include an input shaft, a plurality of traction balls distributed radially around the axis, each traction ball is mounted on an axle passing there through, the axles are tiltable in the radial grooves in the housing and support plate. To control the position of the traction balls, the axles are guided in curved slots of a turnable iris plate. To control the axial placement of the traction balls, there is a rotatable input disc positioned adjacent to the traction balls, a rotatable output disc positioned adjacent to the traction balls opposite the input disc, and a pre-spanning ring around the traction balls such that each of the traction balls is making three-point contact with the input disc, the output disc and the pre-spanning ring, the contact surface of the pre-spanning ring having a specific curvature larger than the radius of the traction balls.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/159,688, filed Jun. 30, 2008, which is a national phase applicationof International Application No. PCT/IB2006/054911, filed Dec. 18, 2006,which claims the benefit of European Application No. 05028709.3, filedDec. 30, 2005. The disclosures of all of the above-referenced priorapplications, publications, and patents are considered part of thedisclosure of this application, and are incorporated by reference hereinin their entirety.

BACKGROUND

Technical Field

The present invention relates to a continuously variable geartransmission of the kind set forth in the preamble of claim 1.

Background Art

In continuously variable gear transmissions of this kind it is known toprovide an axial force generator in the form of a spring to ensure thenecessary contact pressure between the surfaces of the input and outputdiscs and the traction balls. A continuously variable gear transmissionof this kind is e.g. known from U.S. Pat. No. 2,469,653, in which thetension of the spring for providing the necessary contact pressure canbe adjusted by means of a nut.

DISCLOSURE OF THE INVENTION

It is the object of the present invention to provide a variable geartransmission of the kind referred to above, in which the torque transferis improved under varying loads and during fast change of transmissionratio, and having an efficient, simple and compact design compared tothe prior art. This object is achieved with a continuously variable geartransmission of said kind, which according to the present invention alsocomprises the features set forth in the characterising part of claim 1.With this arrangement, the forces from the pre-spanning ring, having acurvature with a radius larger than the radius of the traction balls anda pre-span, will provide the necessary normal forces in the contactpoints when the transmission is running with a constant ratio, in whichsituation the traction balls and the pre-spanning ring will have contactwhere the pre-spanning ring has its largest inner diameter. When thegear transmission ratio is increased by tilting the ball axes, theoutput shaft has to accelerate the driven unit and therefore a highertransfer torque is necessary. The inertia of the driven unit often has asize so that the acceleration torque is larger than the transferredtorque when the gear is not in the transient phase.

The fast tilt of the traction ball axes will make the pre-spanning ringmove axially in the same direction as the ball surface. When thepre-spanning ring moves axially, the normal force will change because ofthe changed inner diameter at the contact point. When the transmissionratio stops changing, the pre-spanning ring will move back to its normalposition with contact point at the largest inner diameter with a speedrelated to the operating speed.

The exact curvature of the inner surface of the pre-spanning ring can bedesigned to match the requirements of the specific usage, e.g. a smallerradius will mean an ability to accelerate units with greater inertia.

The continuously variable gear transmission may further be provided withan axial force generator which will increase the normal forces on thetraction balls when the torque requirements rise, and decrease theforces when the torque requirements fall.

By means of the combination of the axial force generator and thecurvature of the pre-spanning ring, the transmission will automaticallyadjust to the prevailing load situation.

Preferably all forces for providing the required torque are internal andlimited to the input shaft, from the axial force generator to the inputdisc, the traction balls, the pre-spanning ring, the output disc andthrough a thrust bearing back to the input shaft. Thus, these forces arenot transferred through the housing.

The position of the traction balls is controlled by their three-pointcontact, and the angle of the traction ball axles can be controlled by arotatable iris plate. The iris plate is a disc or plate with spiralgrooves, and the iris plate is shaped to fit around the curvature of thetraction balls, keeping a constant distance to the traction balls.

The axles of the traction balls pass through the radial grooves in thesupport plate and the spiral grooves in the iris plate and when the irisplate is rotated, the axles will tilt. In order to provide room for thetilting movement, the grooves in the iris plate are wider than thediameter of the axles and in order to prevent play, the axles are fittedwith iris rollers having a diameter equal to the width of the grooves inthe iris plate. Different systems for rotation of the iris plate can beenvisaged, such as e.g. using a step motor for controlling thetransmission ratio.

If the step motor or similar actuator is connected to the support platewith the radial grooves and the support plate has a minor rotationalplay, the actuator forces under rapid movement can be minimised. Thiswill be explained in the following.

If the axle of each traction ball is lying in a plane through the inputshaft respectively, the balls are performing a pure rolling and the ballaxles are stable.

If the radial grooves in the housing and support plate are not perfectlyaligned, the ball axle is tilted and the ball will behave like a turningwheel on a car. Because is it axially fixed it can only start tilting inthe groove.

This reaction will continue until the ball axles hit the stops in thegrooves and the reaction time and direction will be dependent upon thesize of the misalignment and the turning direction of the support platerelative to the rotational direction of the input disc.

If the rotational direction of the input disc is clockwise and thesupport plate is provided with a small rotation clockwise, the frontends of the ball axles will move towards the rotational axis of theinput shaft, if the support plate is rotated counter clockwise, thefront ends of the ball axles will move away from the rotational axis ofthe input shaft. Thus by controlling the rotational position of thesupport plate it is possible to enforce and support the activation ofthe iris plate.

If the actuator housing is connected to the support plate and theactuator arm is connected to the iris plate, these will always move inopposite directions, and if the support plate is flexibly mounted withsprings forcing it towards the ideal aligned position, the actuatorforces can be kept to a minimum and at the same time providing a quickactuation.

As a simplistic alternative the supporting rotation of the support platecan be provided by means of that part of the force from the iris plateto the traction ball axles, which is not directed in the radialdirection of the grooves in the support plate. This solution will onlyrequire that the turning of the iris plate for reducing the transmissionratio is chosen in accordance with the corresponding rotationaldirection of the input disc, and naturally that the support plate isflexibly mounted with a possibility of a small rotation.

In an alternative embodiment the continuously variable gear transmissionfurther comprises a disengagement mechanism, which lets the driven unitfreewheel relative to the driving unit, when no drive of the driven unitis needed. Preferably the disengagement mechanism is controlled by theiris plate in such a way that with the transmission in its lowest ratiofurther turning of the iris plate keeps the traction ball axles in thesame position and ramps on the iris plate transfers a force through aclutch plate to the input disc, which consequently is disengaged fromthe traction balls, thus disengaging the connection between the drivingunit and the driven unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described more fully below withreference to the drawing, in which

FIG. 1 shows a sectional view of a continuous variable transmissionaccording to the invention seen in the direction A-A in FIG. 2,

FIG. 2 shows a side view of the continuously variable transmissionshowing the radial grooves in the support plate,

FIG. 3 shows the iris plate with spiral grooves,

FIG. 4A shows a sectional view of the axial force generator,

FIG. 4b shows an exploded view of the axial force generator,

FIG. 5A shows a sectional view of the pre-spanning ring and a tractionball, in the constant ratio state,

FIG. 5B shows a sectional view of the pre-spanning ring and a tractionball after a quick tilt of the traction balls axles

FIG. 6A shows the iris plate with modified grooves and ramps for thealternative embodiment with disengagement mechanism,

FIG. 6B shows the iris plate of FIG. 6a in a perspective view moreclearly showing the ramps,

FIG. 7 shows the clutch plate and control pins used in the alternativeembodiment

FIG. 8 shows a sectional view of the continuously gear transmission inaccordance with the alternative embodiment with the disengagementmechanism cut through a traction ball,

FIG. 9 shows a sectional view corresponding to FIG. 8, but cut betweenthe traction balls.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a section through a continuously variable transmissionaccording to an embodiment of the invention. The transmission comprisesan input shaft 1 whose rotation is to be converted into rotation of anoutput shaft 10, whose one end extends out of the gear, said outputshaft 10 being axially aligned with the input stub shaft 1. As shown inFIGS. 4A and 4B, the input shaft 1 is connected by an axial forcegenerator to an input disc 8. The axial force generator consists of anumber of ramps 14 on the input shaft 1, a number of ramps 15 on theinput disc 8 and in between a number of balls 16. This axial forcegenerator provides an axial force varying with the torque of the inputshaft 1. The slope of the ramps 14, 15 is calculated to create an axialforce to result in the needed normal force on the traction balls 2 togive the required traction.

This axial force presses the traction balls 2 towards the pre-spanningring 11. Surface 12 of the pre-spanning ring 11 may be curved. When theinput shaft 1 rotates the traction balls 2, they will start spinning,and the contact point between traction balls 2 and surface 12 ofpre-spanning ring 11 will move to the axial centre of the pre-spanningring 11, where the inner diameter of the pre-spanning ring 11 islargest, as shown in FIG. 5A. When the traction balls 2 are tiltedrapidly, the pre-spanning ring will follow axially and the contact pointwill move to a point with a smaller inner diameter of the pre-spanningring 11, as shown in FIG. 5B, which results in a larger normal force atthe contact points of the traction balls 2.

The positions of the traction balls are defined by the three contactpoints with the input disc 8, pre-spanning ring 11 and output disc 9,and the axles are supported by the grooves in the housing 5 and thesupport plate 6 shown in FIG. 2.

The iris plate 7 shown in FIG. 3 controls the angle of the traction ballaxles 3. The axles 3 of the traction balls 2 supported by the radialgrooves 4 in the housing 5 and the support plate 6 passes through thegrooves 13 in the iris plate 7. When the iris plate 7 turns, the axles 3will tilt, in order to make it possible for the axles 3 to pass throughthe grooves 13 at an angle, the grooves 13 in the iris plate 7 are widerthan the diameter of the friction ball axles 3. To prevent play, thefriction ball axles 3 are equipped with iris rollers 17, which have thesame diameter as the grooves 13 in the iris plate.

The iris plate 18 shown in FIGS. 6A and 6B comprises grooves 19, theinner part of which maintain a constant radius, in order to provide theminimum transmission ratio in connection with disengagement. Thedisengagement is provided by means of the ramps 20 on the iris plate 18,said ramps 20 forcing the clutch plate 21 shown in FIG. 7 towards thethrust bearing 22, when the iris plate 18 is turned further onwardsafter reaching the minimum transmission ratio. The thrust bearing 22will thus push the input disc 8 away from its engagement with thetraction balls 2 whereby the driven unit is disengaged from the drivingunit. In this situation i.e. the disengaged position of the input disc8, the torque on the input shaft 1 will be close to zero and thus if anaxial force generator is present, the axial force will be at a minimum,further supporting the disengagement of the transmission. The rotationalposition of the clutch plate 21 may be controlled by means of pins 23inserted in the housing, whereby the movement of the clutch plate 21 islimited to an axial movement.

The FIGS. 8 and 9 show different cross-sectional views of thetransmission with the disengagement mechanism implemented. In FIG. 8 thecross-sectional view is provided through a traction ball 1 and in FIG. 9a cross-sectional view is provided between the traction balls 1.

Above the invention has been described in connection with a preferredembodiment, however, many deviations may be envisaged without departingfrom the scope of the following claims, such as having the pre-spanningring positioned on the inside of the traction balls 2 and the input andoutput discs positioned with contact on the outside of the tractionballs 2, or other possible mechanisms for tilting the traction balls 2,etc.

What I claim is:
 1. A continuously variable gear transmissioncomprising: a housing; an input shaft connected to an input disc; anoutput shaft connected to an output disc; a plurality of traction ballseach having a radius (r) and being distributed radially around the inputand output discs; a rotatable pre-spanning ring, said traction ballseach being mounted for rotation around a rotation axis, the angle of therotation axes being controlled for controlling the transmission ratio ofthe gear transmission, said traction balls having three-point contactwith the input disc, the output disc, and the pre-spanning ring,respectively, the pre-spanning ring being mounted axially displaceableand having a curvature of the surface in contact with the tractionballs, said curvature being larger than the radius (r) of the tractionballs; and a disengagement mechanism for disengaging the input disc fromthe traction balls, the disengagement being performed with thetransmission in a low gearing position, the disengagement mechanismcomprising ramps provided on an iris plate, said ramps forcing the inputdisc to a position out of engagement with the traction balls.
 2. Acontinuously variable gear transmission in accordance with claim 1, saidtraction balls being mounted on axles for rotation thereon, said axlesextending pivotably through radial grooves in said housing and a supportplate and through spiral grooves in the iris plate for controlling theangles of the axles.
 3. A continuously variable gear transmission inaccordance with claim 1, further comprising an axial force generatorbetween the input shaft and the input disc.
 4. A continuously variablegear transmission in accordance with claim 3, the forces of the axialforce generator being transmitted internally from the input shaft to theinput disc and via the traction balls to the output disc and through athrust bearing back to the input shaft.
 5. A continuously variable geartransmission in accordance with claim 1, further comprising a supportplate having a minor rotational play around its ideal aligned position.6. A continuously variable gear transmission in accordance with claim 1,the pre-spanning ring being positioned on the outside of the tractionballs.
 7. A continuously variable gear transmission in accordance withclaim 1, configured to drive a compressor or a ventilator.
 8. Acontinuously variable gear transmission comprising: a housing; an inputshaft connected to an input disc; an output shaft connected to an outputdisc; a plurality of traction balls each having a radius (r) and beingdistributed radially around the input and output discs, said tractionballs being mounted on axles for rotation thereon, said axles extendingpivotably through radial grooves in said housing and a support plate andthrough spiral grooves in an iris plate for controlling the angles ofthe axles; a rotatable pre-spanning ring, said traction balls each beingmounted for rotation around a rotation axis, the angle of the rotationaxes being controlled for controlling the transmission ratio of the geartransmission, said traction balls having three-point contact with theinput disc, the output disc, and the pre-spanning ring, respectively,the pre-spanning ring being mounted axially displaceable and having acurvature of the surface in contact with the traction balls, saidcurvature being larger than the radius (r) of the traction balls; andramps provided on the iris plate, said ramps forcing the input disc to aposition out of engagement with the traction balls.
 9. A continuouslyvariable gear transmission in accordance with claim 8, furthercomprising a disengagement mechanism for disengaging the input disc fromthe traction balls, the disengagement being performed with thetransmission in a low gearing position.
 10. The continuously variablegear transmission in accordance with claim 8, further comprising anaxial force generator between the input shaft and the input disc. 11.The continuously variable gear transmission in accordance with claim 10,the forces of the axial force generator being transmitted internallyfrom the input shaft to the input disc and via the traction balls to theoutput disc and through a thrust bearing back to the input.
 12. Thecontinuously variable gear transmission in accordance with claim 8, thepre-spanning ring being positioned on the outside of the traction balls.13. A continuously variable gear transmission in accordance with claim8, configured to drive a compressor or a ventilator.